Evaluating Mitigation Options of Nitrous Oxide Emissions in California Cropping Systems.

摘要

Nitrous oxide (N2O), which is produced by soil microorganisms, contributes about 2.6% of California’s (CA) greenhouse gases (GHGs), or one quarter of all GHGs from CA’s agriculture sector. The rates of N2O emissions depend on cropping system nitrogen (N) inputs and biophysical factors that can be influenced by soil management. Previously (ARB contract 08-324), we quantified the N2O emissions in N rate trials in tomato, lettuce, wheat, and rice systems to demonstrate the reductions in emissions possible at proper N fertilization rates. In the present study, we evaluated additional management practices related to N fertilization and irrigation that can be used as N2O emissions mitigation techniques in side-by-side on-farm field experiments that included measurements of yields and N use efficiency in tomato, corn, and lettuce. The treatments included fertilizer N source and placement, use of nitrification inhibitors (NIs), irrigation techniques, and organic management. Use of NIs significantly reduced N2O emissions by 26-63% with reductions in carbon dioxide equivalents (CO2eq), ranging from 72 kg ha-1 in subsurface drip irrigated (SDI) tomato to 1300 kg ha-1 in furrow irrigated (FI) corn. With SDI, reductions in N2O emissions ranged from 265 – 1950 kg CO2eq ha-1, or 60-95%, compared to FI, while surface drip and sprinkler irrigation in lettuce produced mixed results. Among fertilizer N sources, N2O emissions decreased in the order aqua ammonia (aq.A.) > urea ammonium nitrate (UAN) > calcium nitrate. Applying UAN fertilizer in two bands per corn row instead of one also reduced N2O emissions. Total GHG emissions were similar with conventional and organic management. Incentives to expand the acreage under SDI, the use of NIs in systems where ammonical fertilizers are spatially and temporally concentrated, and measures that increase nitrogen use efficiency are recommended as GHG mitigation strategies that will either increase or not affect crop performance.